1. Field of the Invention
The present invention relates to a control apparatus and method which detects operation status of a control object and feedback-controls the control object such that the operation status becomes as desired.
2. Description of Related Art
A conventional control apparatus detects an operation status of a control object by using a sensor or the like, calculates a control amount for controlling the control object by using the difference between the detected actual operation status and desired status and a predetermined control gain (i.e., feedback gain), and feedback-controls the control object by the calculated control amount.
In this control apparatus, when the difference between the actual operation status of the control object and the desired status is large, the control object can be quickly changed toward the desired status by increasing the control gain. This improves the control response. However, when the actual operation status is close to the desired status, overshoot or undershoot (collectively referred to as overshoot) that the actual operation status exceeds the desired status occurs. It takes a significant amount of time to converge the operation status to the desired status. On the other hand, if the control gain is reduced, the overshoot problem can be prevented, to improve the control stability. However, the control response is lowered.
To overcome those problems, for example, in a constant-speed running apparatus which feedback-controls the running speed of a vehicle to a target speed, a running resistance (i.e., external load on a control object) is determined from an acceleration or the like of the vehicle as the control object, and a control gain is varied with the determined running resistance to prevent overshoot (U.S. Pat. No. 5,392,215 and JP-A 6-64461). At the beginning of overshoot, the control gain is changed to improve the control convergence after the occurrence of overshoot (JP-A 3-22734). Overshoot is prevented by setting the control gain in accordance with the vehicle acceleration upon start of control (U.S. Pat. No. 4,725,969 and JP-A 60-71341).
Further, other controls than those in the constant-speed running device have been proposed. For example, in idle rotation control and the like to control an idle rotation speed of an internal combustion engine to a target idle rotation speed, overshoot can be prevented by setting a control gain in accordance with the difference between the desired status (target idle rotation speed) and actual operation status (actual idle rotation speed).
That is, in the conventional control apparatuses, to prevent overshoot while ensuring control response, the control gain is set based on an external load on the control object or the operation of the control object upon start of control, or based on the difference between the desired status and the actual operation status during control.
However, as these conventional apparatuses set the control gain from operation status or the like of the control object, requirements for both the improved control response and control stability cannot be sufficiently satisfied.